Method of polycarbonate preparation

ABSTRACT

Polycarbonates containing low or undetectable levels of Fries rearrangement products and comprising repeat units derived from one or more of resorcinol, hydroquinone, methylhydroquinone, bisphenol A, and 4,4′-biphenol have been prepared by the melt reaction of one or more of the aforementioned dihydroxy aromatic compounds with an ester-substituted diaryl carbonate such as bis-methyl salicyl carbonate. Low, or in many instances undetectable, levels of Fries rearrangement products are found in the product polycarbonates obtained as the combined result of a highly effective catalyst system which suppresses the Fries reaction and the use of lower melt polymerization temperatures relative to temperatures required for the analogous polymerization reactions using diphenyl carbonate.

PRIORITY CLAIM

This application is a continuation of PCT/US2003/039139 (IPNWO2004/060962) filed on Dec. 10, 2003, which designates the US andclaims priority to U.S. application Ser. No. 10/326,933 filed on Dec.23, 2002, now U.S. Pat. No. 6,870,025, which is a continuation-in-partof U.S. application Ser. No. 09/911,443 filed Jul. 24, 2001, now U.S.Pat. No. 6,548,623, all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

This invention relates to the preparation of polycarbonates by the meltreaction of a dihydroxy aromatic compound with an ester-substituteddiaryl carbonate. More particularly, the instant invention relates tothe formation under mild conditions of polycarbonates having extremelylow levels of Fries rearrangement products and possessing a high levelof endcapping.

Polycarbonates, such as bisphenol A polycarbonate, are typicallyprepared either by interfacial or melt polymerization methods. Thereaction of a bisphenol such as bisphenol A (BPA) with phosgene in thepresence of water, a solvent such as methylene chloride, an acidacceptor such as sodium hydroxide and a phase transfer catalyst such astriethylamine is typical of the interfacial methodology. The reaction ofbisphenol A with a source of carbonate units such as diphenyl carbonateat high temperature in the presence of a catalyst such as sodiumhydroxide is typical of currently employed melt polymerization methods.Each method is practiced on a large scale commercially and each presentssignificant drawbacks.

The interfacial method for making polycarbonate has several inherentdisadvantages. First it is a disadvantage to operate a process whichrequires phosgene as a reactant due to obvious safety concerns. Secondit is a disadvantage to operate a process, which requires using largeamounts of an organic solvent because expensive precautions must betaken to guard against any adverse environmental impact. Third, theinterfacial method requires a relatively large amount of equipment andcapital investment. Fourth, the polycarbonate produced by theinterfacial process is prone to having inconsistent color, higher levelsof particulates, and higher chloride content, which can cause corrosion.

The melt method, although obviating the need for phosgene or a solventsuch as methylene chloride requires high temperatures and relativelylong reaction times. As a result, by-products may be formed at hightemperature, such as the products arising by Fries rearrangement ofcarbonate units along the growing polymer chains. Fries rearrangementgives rise to undesired and uncontrolled polymer branching which maynegatively impact the polymer's flow properties and performance.

Some years ago, it was reported in U.S. Pat. No. 4,323,668 thatpolycarbonate could be formed under relatively mild conditions byreacting a bisphenol such as BPA with the diaryl carbonate formed byreaction of phosgene with methyl salicylate. The method used relativelyhigh levels of transesterification catalysts such as lithium stearate inorder to achieve high molecular weight polycarbonate. High catalystloadings are particularly undesirable in melt polycarbonate reactionssince the catalyst remains in the product polycarbonate following thereaction. The presence of a transesterification catalyst in a thepolycarbonate may shorten the useful life span of articles madetherefrom by promoting increased water absorption, polymer degradationat high temperatures and discoloration.

It would be desirable, therefore, to minimize the amount of catalystrequired in the for the melt preparation of polycarbonate frombisphenols and ester substituted diaryl carbonates such as bis-methylsalicyl carbonate. The present invention provides a method which confersthese and other advantages upon the preparation of polycarbonate via themelt polymerization process.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method of preparing a polycarbonate,said method comprising heating a mixture comprising a catalyst, at leastone diaryl carbonate having structure I

wherein R¹ and R² are independently C₁–C₂₀ alkyl radicals, C₄–C₂₀cycloalkyl radicals, or C₄–C₂₀ aromatic radicals,R³ and R⁴ are independently at each occurrence a halogen atom, cyanogroup, nitro group, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical,C₄–C₂₀ aromatic radical, C₁–C₂₀ alkoxy radical, C₄–C₂₀ cycloalkoxyradical, C₄–C₂₀ aryloxy radical, C₁–C₂₀ alkylthio radical, C₄–C₂₀cycloalkylthio radical, C₄–C₂₀ arylthio radical, C₁–C₂₀ alkylsulfinylradical, C₄–C₂₀ cycloalkylsulfinyl radical, C₄–C₂₀ arylsulfonyl radical,C₁–C₂₀ alkylsulfonyl radical, C₄–C₂₀ cycloalkylsulfonyl radical, C₄–C₂₀arylsulfonyl radical, C₁–C₂₀ alkoxycarbonyl radical, C₄–C₂₀cycloalkoxycarbonyl radical, C₄–C₂₀ aryloxycarbonyl radical, C₂–C₆₀alkylamino radical, C₆–C₆₀ cycloalkylamino radical, C₅–C₆₀ arylaminoradical, C₁–C₄₀ alkylaminocarbonyl radical, C₄–C₄₀cycloalkylaminocarbonyl radical, C₄–C₄₀ arylaminocarbonyl radical, orC₁–C₂₀ acylamino radical, and b and c are independently integers 0–4;and at least one dihydroxy aromatic compound selected from the groupconsisting of resorcinol, methylresorcinol, hydroquinone, andmethylhydroquinone, said catalyst comprising at least one source ofalkaline earth ions or alkali metal ions, and at least one quaternaryammonium compound, quaternary phosphonium compound, or a mixturethereof, said source of alkaline earth ions or alkali metal ions beingpresent in an amount such that between about 1×10⁻⁵ and about 1×10⁻⁸moles of alkaline earth metal ions or alkali metal ions are present inthe mixture per mole of dihydroxy aromatic compound employed, saidquaternary ammonium compound, quaternary phosphonium compound, ormixture thereof being present in an amount between about 2.5×10⁻³ andabout 1×10⁻⁶ moles per mole of dihydroxy aromatic compound employed, toprovide a product polycarbonate, said product polycarbonate comprisingrepeat units derived from at least one member of the group consisting ofresorcinol, methylresorcinol, hydroquinone, and methylhydroquinone.

The present invention further relates to a method for formingpolycarbonates by reaction of an ester-substituted diaryl carbonate inwhich the level of Fries rearrangement product in the productpolycarbonate is less than about 1000 parts per million (ppm) and thelevel of internal ester carbonate linkages in the product polycarbonateis less than about 1 percent of the total number of moles of dihydroxyaromatic compound employed and the level of terminal hydroxy estergroups in the product polycarbonate is less than about 1 percent of thetotal number of moles of dihydroxy aromatic compound employed.

DETAILED DESCRIPTION OF THE INVENTION

The present invention may be understood more readily by reference to thefollowing detailed description of preferred embodiments of the inventionand the examples included therein. In the following specification andthe claims which follow, reference will be made to a number of termswhich shall be defined to have the following meanings:

The singular forms “a”, “an” and “the” include plural referents unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

As used herein the term “polycarbonate” refers to polycarbonatesincorporating structural units derived from one or more dihydroxyaromatic compounds and includes copolycarbonates and polyestercarbonates.

As used herein, the term “melt polycarbonate” refers to a polycarbonatemade by the transesterification of a diaryl carbonate with at least onedihydroxy aromatic compound.

“BPA” is herein defined as bisphenol A or2,2-bis(4-hydroxyphenyl)propane.

As used herein the terms “4,4′-dihydroxy-1,1-biphenyl” and“4,4′-biphenol” have the same meaning and refer to the same compound(CAS No. 92-88-6).

As used herein the term “methylresorcinol” refers to any one of thethree isomers of methylresorcinol, 2-methylresorcinol,4-methylresorcinol, and 5-methyresorcinol. The 5-methyl isomer ofresorcinol, 5-methyl resorcinol, is also known as orcinol.

“Catalyst system” as used herein refers to the catalyst or catalyststhat catalyze the transesterification of the bisphenol with the diarylcarbonate in the melt process.

As used herein, the terms “dihydroxy aromatic compound”, “bisphenol”,“diphenol” and “dihydric phenol” are synonymous.

“Catalytically effective amount” refers to the amount of the catalyst atwhich catalytic performance is exhibited.

As used herein the term “Fries product” is defined as a structural unitof the product polycarbonate which upon hydrolysis of the productpolycarbonate affords a carboxy-substituted dihydroxy aromatic compoundbearing a carboxy group adjacent to one or both of the hydroxy groups ofsaid carboxy-substituted dihydroxy aromatic compound. For example, inbisphenol A polycarbonate prepared by a melt reaction method in whichFries reaction occurs, among the Fries products within the productpolycarbonate are those structural units, for example structure VIIIbelow, which afford 2-carboxy bisphenol A upon complete hydrolysis ofthe product polycarbonate.

The terms “Fries product” and “Fries group” are used interchangeablyherein.

The terms “Fries reaction” and “Fries rearrangement” are usedinterchangeably herein.

As used herein the term “aliphatic radical” refers to a radical having avalence of at least one comprising a linear or branched array of atomswhich is not cyclic. The array may include heteroatoms such as nitrogen,sulfur and oxygen or may be composed exclusively of carbon and hydrogen.Examples of aliphatic radicals include methyl, methylene, ethyl,ethylene, hexyl, hexamethylene and the like.

As used herein the term “aromatic radical” refers to a radical having avalence of at least one comprising at least one aromatic group. Examplesof aromatic radicals include phenyl, pyridyl, furanyl, thienyl,naphthyl, phenylene, and biphenyl. The term includes groups containingboth aromatic and aliphatic components, for example a benzyl group.

As used herein the term “cycloaliphatic radical” refers to a radicalhaving a valance of at least one comprising an array of atoms which iscyclic but which is not aromatic. The array may include heteroatoms suchas nitrogen, sulfur and oxygen or may be composed exclusively of carbonand hydrogen. Examples of cycloaliphatic radicals include cyclopropyl,cyclopentyl cyclohexyl, tetrahydrofuranyl and the like.

In the present invention it has been discovered that extremely lowlevels of catalyst may be employed to prepare polycarbonate using themelt reaction of an ester substituted diaryl carbonate with a dihydroxyaromatic compound. The use of very low catalyst loadings is desirablefrom at least two perspectives. First, the use of low catalyst levelsduring melt polymerization tends to suppress the formation of undesiredFries rearrangement products. Second, because residual catalyst presentin the polymer tends to decrease the useful life-span of articles madefrom it by increasing water absorption, decreasing thermal stability andpromoting discoloration, its minimization is desirable. Thepolycarbonate prepared by the method of the present invention istypically free of, or contains undetectable levels of Friesrearrangement products. Moreover, in the absence of an added exogenousmonofunctional phenol the product polycarbonate is very highly endcappedwith less than 50% of the endgroups being free hydroxyl groups. Where anexogenous monofunctional phenol is added to the polymerization mixture,high levels of incorporation of said phenol are observed. In this mannerboth the identity of the polymer endgroups and the polymer molecularweight may be controlled in the melt reaction.

In the process of the present invention an ester-substituted diarylcarbonate having structure I is reacted under melt reaction conditionswith at least one dihydroxy aromatic compound in the presence of atleast one source of alkaline earth ions or alkali metal ions, and anorganic ammonium compound or an organic phosphonium compound, or acombination thereof. Ester-substituted diaryl carbonates I areexemplified by bis-methyl salicyl carbonate (CAS Registry No.82091-12-1), bis-ethyl salicyl carbonate, bis-propyl salicyl carbonate,bis-butyl salicyl carbonate, bis-benzyl salicyl carbonate, bis-methyl4-chlorosalicyl carbonate and the like. Typically bis-methyl salicylcarbonate is preferred.

The dihydroxy aromatic compounds used according to the method of thepresent invention include at least one dihydroxy aromatic compoundselected from the group consisting of resorcinol, methylresorcinol,hydroquinone, and methylhydroquinone. The product polycarbonate preparedaccording to the method of the present invention thus comprises repeatunits derived from at least one member of the group consisting ofresorcinol, methylresorcinol, hydroquinone, and methylhydroquinone. Thepresent invention provides a method for the preparation ofhomopolycarbonates, and polycarbonates comprising repeat units derivedfrom two or more dihydroxy aromatic compounds.

The polycarbonates prepared according to the method of the presentinvention may further comprise repeat units derived from a variety ofdihydroxy aromatic compounds in addition to resorcinol,methylresorcinol, hydroquinone, and methylhydroquinone. For example,polycarbonates prepared according to the method of the present inventionmay also comprise repeat units derived from dihydroxy aromatic compoundsselected from the group consisting of bisphenols having structure II,

wherein R⁵–R¹² are independently a hydrogen atom, halogen atom, nitrogroup, cyano group, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, orC₆–C₂₀ aryl radical,W is a bond, an oxygen atom, a sulfur atom, a SO₂ group, a C₆–C₂₀aromatic radical, a C₆–C₂₀ cycloaliphatic radical, or the group

wherein R¹³ and R¹⁴ are independently a hydrogen atom, C₁–C₂₀ alkylradical, C₄–C₂₀ cycloalkyl radical, or C₄–C₂₀ aryl radical, or R¹³ andR¹⁴ together form a C₄–C₂₀ cycloaliphatic ring which is optionallysubstituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀ aryl, C₅–C₂₁ aralkyl,C₅–C₂₀ cycloalkyl groups, or a combination thereof;dihydroxy benzenes having structure III

wherein R¹⁵ is independently at each occurrence a hydrogen atom, halogenatom, nitro group, cyano group, C₂–C₂₀ alkyl radical, C₄–C₂₀ cycloalkylradical, or a C₄–C₂₀ aryl radical, and d is an integer from 1 to 4; anddihydroxy naphthalenes having structures IV and V

wherein R¹⁶,R¹⁷,R¹⁸ and R¹⁹ are independently at each occurrence ahydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkylradical, C₄–C₂₀ cycloalkyl radical, or a C₄–C₂₀ aryl radical, e and fare integers of from 0 to 3, g is an integer from 0 to 4, and h is aninteger from 0 to 2.

Suitable bisphenols II are illustrated by2,2-bis(4-hydroxyphenyl)propane (bisphenol A);2,2-bis(3-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-3-methylphenyl)propane;2,2-bis(4-hydroxy-3-isopropylphenyl)propane;2,2-bis(3-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane;2,2-bis(3-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane;2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane;2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane;2,2-bis(3-chloro-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-methylphenyl)propane;2,2-bis(3-chloro-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-bromo-4-hydroxy-5-isopropylphenyl)propane;2,2-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3-chloro-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3-bromo-5-phenyl-4-hydroxyphenyl)propane;2,2-bis(3,5-disopropyl-4-hydroxyphenyl)propane;2,2-bis(3,5-di-t-butyl-4-hydroxyphenyl)propane;2,2-bis(3,5-diphenyl-4-hydroxyphenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)propane;2,2-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)propane;2,2-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)propane;2,2-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)cyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)cyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)cyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-chloro-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)cyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)cyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-3-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dichloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dibromo-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-methylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-chloro-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-4-hydroxy-5-isopropylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-t-butyl-5-chloro-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;bis(3-chloro-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3-bromo-5-phenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-disopropyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-di-t-butyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(3,5-diphenyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrachlorophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetrabromophenyl)-3,3,5-trimethylcyclohexane;1,1-bis(4-hydroxy-2,3,5,6-tetramethylphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dichloro-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;1,1-bis(2,6-dibromo-3,5-dimethyl-4-hydroxyphenyl)-3,3,5-trimethylcyclohexane;4,4′-dihydroxy-1,1-biphenyl (4,4′-biphenol);4,4′-dihydroxy-3,3′-dimethyl-1,1-biphenyl;4,4′-dihydroxy-3,3′-dioctyl-1,1-biphenyl; 4,4′-dihydroxydiphenylether;4,4′-dihydroxydiphenylthioether;1,3-bis(2-(4-hydroxyphenyl)-2-propyl)benzene;1,3-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene;1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene,1,4-bis(2-(4-hydroxy-3-methylphenyl)-2-propyl)benzene;bis(4-hydroxyphenyl)methane; 1,1-bis(4-hydroxyphenyl)ethane;2,2-bis(4-hydroxyphenyl)butane; 2,2-bis(4-hydroxyphenyl)octane; and1,1-bis(4-hydroxyphenyl)cyclopentane;

Suitable dihydroxy benzenes III are illustrated by 5-phenyl resorcinol,5-butylresorcinol, 2-hexylresorcinol, 4-hexylresorcinol,5-hexylresorcinol, ethylhydroquinone, butylhydroquinone,hexylhydroquinone, phenylhydroquinone, 4-phenylresorcinol, and4-ethylresorcinol.

Suitable dihydroxy naphthalenes IV are illustrated by2,6-dihydroxynaphthalene; 2,6-dihydroxy-3-methylnaphthalene; and2,6-dihydroxy-3-phenylnaphthalene.

Suitable dihydroxy naphthalenes V are illustrated by1,4-dihydroxynaphthalene; 1,4-dihydroxy-2-methylnaphthalene;1,4-dihydroxy-2-phenylnaphthalene and 1,3-dihydroxynaphthalene.

The catalyst used in the method of the present invention comprises atleast one source of alkaline earth ions or alkali metal ions, and atleast one quaternary ammonium compound, quaternary phosphonium compound,or a mixture thereof, said source of alkaline earth ions or alkali metalions being used in an amount such that the amount of alkaline earth oralkali metal ions present in the reaction mixture is in a range betweenabout 1×10⁻⁵ and about 1×10⁻⁸ moles alkaline earth or alkali metal ionper mole of dihydroxy aromatic compound employed.

The quaternary ammonium compound is selected from the group of organicammonium compounds having structure VI

wherein R²⁰–R²³ are independently a C₁–C₂₀ alkyl radical, C₄–C₂₀cycloalkyl radical, or a C₄–C₂₀ aryl radical, and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isselected from the group consisting of hydroxide, halide, carboxylate,sulfonate, sulfate, formate, carbonate, and bicarbonate.

Suitable organic ammonium compounds comprising structure VI areillustrated by tetramethylammonium hydroxide, tetrabutylammoniumhydroxide, tetramethylammonium acetate, tetramethylammonium formate andtetrabutylammonium acetate.

The quaternary phosphonium compound is selected from the group oforganic phosphonium compounds having structure VII

wherein R²⁴–R²⁷ are independently a C₁–C₂₀ alkyl radical, C₄–C₂₀cycloalkyl radical, or a C₄–C₂₀ aryl radical, and X⁻ is an organic orinorganic anion. In one embodiment of the present invention anion X⁻ isan anion selected from the group consisting of hydroxide, halide,carboxylate, sulfonate, sulfate, formate, carbonate, and bicarbonate.

Suitable organic phosphonium compounds comprising structure VII areillustrated by tetramethylphosphonium hydroxide, tetramethylphosphoniumacetate, tetramethylphosphonium formate, tetrabutylphosphoniumhydroxide, and tetrabutylphosphonium acetate.

Where X⁻ is a polyvalent anion such as carbonate or sulfate it isunderstood that the positive and negative charges in structures VI andVII are properly balanced. For example, where R²⁰–R²³ in structure VIare each methyl groups and X⁻ is carbonate, it is understood that X⁻represents ½ (CO₃ ⁻²).

Suitable sources of alkaline earth ions include alkaline earthhydroxides such as magnesium hydroxide and calcium hydroxide. Suitablesources of alkali metal ions include the alkali metal hydroxidesillustrated by lithium hydroxide, sodium hydroxide, and potassiumhydroxide. Other sources of alkaline earth and alkali metal ions includesalts of carboxylic acids, such as sodium acetate, and derivatives ofethylene diamine tetraacetic acid (EDTA) such as EDTA tetrasodium salt,and EDTA magnesium disodium salt.

In the method of the present invention an ester-substituted diarylcarbonate I, at least one dihydroxy aromatic compound selected from thegroup consisting of resorcinol, methylresorcinol, hydroquinone andmethylhydroquinone, and a catalyst are contacted in a reactor suitablefor conducting melt polymerization. The relative amounts ofester-substituted diaryl carbonate and dihydroxy aromatic compound aresuch that the molar ratio of diaryl carbonate I to dihydroxy aromaticcompound is in a range between about 1.20 and about 0.8, preferablybetween about 1.10 and about 0.9 and still more preferably between about1.05 and about 1.01.

The amount of catalyst employed is such that the amount of alkalineearth metal ion or alkali metal ions present in the reaction mixture isin a range between about 1×10⁻⁵ and about 1×10⁻⁸, preferably betweenabout 5×10⁻⁵ and about 1×10⁻⁷, and still more preferably between about5×10⁻⁵ and about 5×10⁻⁷ moles of alkaline earth metal ion or alkalimetal ion per mole dihydroxy aromatic compound employed. The quaternaryammonium compound, quaternary phosphonium compound or a mixture thereofis used in an amount corresponding to about 2.5×10⁻³ and 1×10⁻⁶ molesper mole dihydroxy aromatic compound employed.

Typically the ester-substituted diaryl carbonate, one or more dihydroxyaromatic compounds and the catalyst are combined in a reactor which hasbeen treated to remove adventitious contaminants capable of catalyzingboth the transesterification and Fries reactions observed inuncontrolled melt polymerizations of diaryl carbonates with dihydroxyaromatic compounds. Contaminants such as sodium ion adhering to thewalls of a glass lined reactor are typical and may be removed by soakingthe reactor in mild acid, for example 3 normal hydrochloric acid,followed by removal of the acid and soaking the reactor in high puritywater, such as deionized water.

In one embodiment of the present invention an ester-substituted diarylcarbonate, such as bis-methyl salicyl carbonate, one or more dihydroxyaromatic compounds, and a catalyst comprising alkali metal ions, such assodium hydroxide, and a quaternary ammonium compound, such astetramethylammonium hydroxide, or a quaternary phosphonium compound,such as tetrabutylphosphonium acetate, are charged to a reactor and thereactor is purged with an inert gas such as nitrogen or helium. Thereactor is then heated to a temperature in a range between about 100° C.and about 340° C., preferably between about 100° C. and about 280° C.,and still more preferably between about 140° C. and about 240° C. for aperiod of from about 0.25 to about 5 hours, preferably from about 0.25to about 2 hours, and still more preferably from about 0.25 hours toabout 1.25 hours. While the reaction mixture is heated the pressure overthe reaction mixture is gradually reduced from ambient pressure to afinal pressure in a range between about 0.001 mmHg and about 400 mmHg,preferably 0.01 mmHg and about 100 mmHg, and still more preferably about0.1 mmHg and about 10 mmHg.

Control of the pressure over the reaction mixture allows the orderlyremoval of the phenolic by-product formed when the dihydroxy aromaticcompound undergoes a transesterification reaction with a species capableof releasing a phenolic by-product, for example bis-methyl salicylcarbonate or a growing polymer chain endcapped by a methyl salicylgroup. As noted above the reaction may be conducted at subambientpressure. In an alternate embodiment of the present invention, thereaction may be conducted at slightly elevated pressure, for example apressure in a range between about 1 and about 2 atmospheres.

As noted, the use of excessive amounts of catalyst may adversely affectthe structure and properties of a polycarbonate prepared under meltpolymerization conditions. The present invention provides a method ofmelt polymerization employing a highly effective catalyst systemcomprising at least one source of alkaline earth or alkali metal ions,and a quaternary ammonium compound or quaternary phosphonium compound,or mixture thereof which provides useful reaction rates at very lowcatalyst concentrations, thereby minimizing the amount of residualcatalyst remaining in the product polycarbonate. Limiting the amount ofcatalyst employed according to the method of the present inventionprovides a new and useful means of controlling the structural integrityof the product polycarbonate as well. Thus, in one embodiment, themethod of the present invention provides a product polycarbonate havinga weight average molecular weight, as determined by gel permeationchromatography, in a range between about 10,000 and about 100,000Daltons, preferably between about 15,000 and about 60,000 Daltons, andstill more preferably between about 15,000 and about 50,000 Daltons saidproduct polycarbonate having less than about 1000, preferably less thanabout 500, and still more preferably less than about 100 parts permillion (ppm) Fries product. Structure VIII illustrates the Friesproduct structure present in a polycarbonate prepared from bisphenol A.

As indicated, the Fries product may serve as a site for polymerbranching, the wavy lines indicating polymer chain structure.

In addition to providing a product polycarbonate containing only verylow levels of Fries products, the method of the present inventionprovides polycarbonates containing very low levels of other undesirablestructural features which arise from side reactions taking place duringmelt the polymerization reaction between ester-substituted diarylcarbonates I and dihydroxy aromatic compounds. One such undesirablestructural feature has structure IX and is termed an internalester-carbonate linkage. In structure IX “R³” and “b” are defined as instructure I. Structure IX is thought to arise by reaction of anester-substituted phenol by-product, for example methyl salicylate, atits ester carbonyl group with a dihydroxy aromatic compound or a hydroxygroup of a growing polymer chain. Further reaction of theester-substituted phenolic hydroxy group leads to formation of

a carbonate linkage. Thus, the ester-substituted phenol by-product ofreaction of an ester-substituted diaryl carbonate with a dihydroxyaromatic compound, may be incorporated into the main chain of a linearpolycarbonate. The presence of uncontrolled amounts of ester carbonatelinkages in the polycarbonate polymer chain is undesirable.

Another undesirable structural feature present in melt polymerizationreactions between ester-substituted diaryl carbonates and dihydroxyaromatic compounds is the ester-linked terminal group having structure Xwhich possesses a free hydroxyl group. In structure X “R³” and “b” aredefined as in structure I. Structure X is thought to arise in the samemanner as structure IX but without further reaction of theester-substituted phenolic hydroxy

group. The presence of uncontrolled amounts of hydroxy terminated groupssuch as X is undesirable. In structures VIII, IX and X the wavy lineshown as represents the product polycarbonate polymer chain structure.

The present invention, in sharp contrast to known methods of effectingthe melt polymerization of an ester-substituted diaryl carbonate and adihydroxy aromatic compound, provides a means of limiting the formationof internal ester-carbonate linkages having structure IX as well asester-linked terminal groups having structure X, during meltpolymerization. Thus in a product polycarbonate prepared using themethod of the present invention structures, IX and X, when present,represent less than 1 mole percent of the total amount of all structuralunits present in the product polymer derived from dihydroxy aromaticcompounds employed as starting materials for the polymer synthesis.

An additional advantage of the method of the present invention overearlier methods of melt polymerization of ester-substituted diarylcarbonates and dihydroxy aromatic compounds, derives from the fact thatthe product polymer is endcapped with ester-substituted phenoxyendgroups and contains very low levels, less than about 50 percent,preferably less than about 10 percent, and still more preferably lessthan about 1 percent, of polymer chain ends bearing free hydroxy groups.The ester substituted terminal groups are sufficiently reactive to allowtheir displacement by other phenols such as p-cumylphenol. Thus,following the melt polymerization the product polycarbonate may betreated with one or more exogenous phenols to afford a polycarbonateincorporating endgroups derived from the exogenous phenol. The reactionof the ester substituted terminal groups with the exogenous phenol maybe carried out in a first formed polymer melt or in a separate step.

In one embodiment of the present invention an exogenous monofunctionalphenol, for example p-cumylphenol, is added at the outset of thereaction between the ester substituted diaryl carbonate and thedihydroxy aromatic compound. The product polycarbonate then containsendgroups derived from the exogenous monofunctional phenol. Theexogenous monofunctional phenol serves both to control the molecularweight of the product polycarbonate and to determine the identity of thepolymer endgroups. The exogenous monofunctional phenol may be added inamounts ranging from about 0.1 to about 10 mole percent, preferably fromabout 0.5 to about 8 mole percent and still more preferably from about 1to about 6 mole percent based on the total number of moles ofdihydroxyaromatic compound employed in the polymerization. Additionalcatalyst is not required apart from the catalytically effective amountadded to effect the polymerization reaction. Suitable exogenousmonofunctional phenols are exemplified by p-cumylphenol; 2,6-xylenol;4-t-butylphenol; p-cresol; 1-naphthol; 2-naphthol; cardanol;3,5-di-t-butylphenol; p-nonylphenol; p-octadecylphenol; and phenol. Inalternative embodiments of the present invention the exogenousmonofunctional phenol may be added at an intermediate stage of thepolymerization or after its completion. In such alternative embodimentsthe exogenous phenol may exert a controlling effect upon the molecularweight of the product polycarbonate and will control the identity of thepolymer terminal groups.

The present invention may be used to prepare polycarbonate productshaving very low levels (less than 1 ppm) of trace contaminants such asiron, chloride ion, and sodium ion. Where such extremely low levels oftrace contaminants is desired it is sufficient to practice the inventionusing starting materials, ester-substituted diary carbonate anddihydroxy aromatic compound having correspondingly low levels of thetrace contaminants in question. For example, the preparation bisphenol Apolycarbonate containing less than 1 ppm each of iron, chloride ion andsodium ion may be made by the method of the present invention usingstarting materials bis-methyl salicyl carbonate and bisphenol Acontaining less than 1 ppm iron, chloride ion and sodium ion.

The method of the present invention can be conducted as a batch or acontinuous process. Any desired apparatus can be used for the reaction.The material and the structure of the reactor used in the presentinvention is not particularly limited as long as the reactor has anordinary capability of stirring and the presence of adventitiouscatalysts can be controlled. It is preferable that the reactor iscapable of stirring in high viscosity conditions as the viscosity of thereaction system is increased in later stages of the reaction.

Polycarbonates prepared using the method of the present invention may beblended with conventional additives such as heat stabilizers, moldrelease agents and UV stabilizers and molded into various moldedarticles such as optical disks, optical lenses, automobile lampcomponents and the like. Further, the polycarbonates prepared using themethod of the present invention may be blended with other polymericmaterials, for example, other polycarbonates, polyestercarbonates,polyesters and olefin polymers such as ABS. In one embodiment apolycarbonate prepared by the method of the present invention is blendedwith one or more polymeric substances to form a polymer bend which maythen molded into a molded article. Thus in one aspect, the presentinvention comprises a molded article prepared from a polymer blendcomprising a polycarbonate prepared by the method of the presentinvention. Molded articles are exemplified by compact disks, automobileheadlamp covers, football helmets and the like.

EXAMPLES

The following examples are set forth to provide those of ordinary skillin the art with a detailed description of how the methods claimed hereinare evaluated, and are not intended to limit the scope of what theinventors regard as their invention. Unless indicated otherwise, partsare by weight, temperature is in ° C.

General Experimental Methods

Molecular weights are reported as number average (M_(n)) or weightaverage (M_(w)) molecular weight and were determined by gel permeationchromatography (GPC), and, unless otherwise indicated, were determinedusing a polycarbonate molecular weight standard to construct a broadstandard calibration curve against which polymer molecular weights weredetermined. The temperature of the gel permeation columns was about 25°C. and the mobile phase was chloroform.

Fries content was measured by the KOH methanolysis of resin and isreported as parts per million (ppm). The Fries content for each of themelt polycarbonates listed in Table 1 was determined as follows. First,0.50 grams of polycarbonate was dissolved in 4.0 ml of THF (containingp-terphenyl as internal standard). Next, 3.0 ml of 18% KOH in methanolwas added to this solution. The resulting mixture was stirred for twohours at ambient temperature. Next, 1.0 ml of acetic acid was added, andthe mixture was stirred for 5 minutes. Potassium acetate by-product wasallowed to crystallize over 1 hour. The solid was filtered off and theresulting filtrate was analyzed by liquid chromatography usingp-terphenyl as the internal standard.

Internal ester-carbonate and terminal hydroxy-ester groups were measuredby ¹³C- and ³¹P-NMR respectively. Terminal hydroxy ester groups werefirst derivatized with 2-chloro-1,3,2-dioxaphospholane (Aldrich).

Melt polymerization reactions were typically run in a 100 mL glassreactor adapted for distillation under vacuum. The reactor was equippedwith a solid nickel helical agitator. The reactor was configured suchthat by-product phenol or methyl salicylate could be distilled out ofthe reaction vessel and condensed in a chilled receiving vessel. Priorto its use, the reactor was soaked in 3N HCl for a period of 12 hoursand was then soaked for an additional 12 hours in deionized water(18-Mohm) and placed in a drying oven overnight. Reaction temperaturewas controlled by immersion of the reactor into a fluidized sand bathequipped with a PID temperature controller. The temperature of the sandbath was monitored at the reactor sand bath interface. The pressure ofthe reaction vessel was controlled by means of a vacuum pump coupled toa nitrogen bleed. The pressure within the reactor was measured with anMKS pirani gauge. Sodium hydroxide (J. T. Baker, 1×10⁻⁶ mole per moledihydroxy aromatic compound) and tetramethylammonium hydroxide (Sachem,2.5×10⁻⁴ mole per mole dihydroxy aromatic compound) ortetrabutylphosphonium acetate (Sachem, 2.5×10⁻⁴ mole per mole dihydroxyaromatic compound) were added as solutions in deionized (18 Mohm) water.Where the catalyst level was varied, the concentration of the catalystsolution was adjusted such that the volume of water introduced in thecatalyst introduction step was held constant.

Examples 1–3 and Comparative Examples 1–4

The reactor was charged at ambient temperature and pressure with solidbisphenol A (General Electric Plastics Japan Ltd., 0.08761 mol) andsolid bis-methyl salicyl carbonate (0.0880–0.0916 mol) or solid diphenylcarbonate (General Electric Plastics Japan Ltd., 0.0946 mol). In someinstances a monofunctional phenol such as p-cumylphenol (0.0027–0.0088mol) was added in order to limit the molecular weight of the polymer andcontrol chain endgroup identity. The catalyst was then injected into thebisphenol A layer and the reactor was assembled. The reactor was thenevacuated briefly and nitrogen was reintroduced. This step was repeatedthree times. The reactor was then lowered into the sand bath maintainedat 180° C. After a five minute period stirring at 250 rpm was initiated.After a total of 10 minutes the reaction mixture had fully melted. Thetemperature of the bath was raised to 210° C. over a five minute period.The pressure in the reactor was then reduced to 180 mmHg at which pointthe phenolic by-product began to distill from the reaction vessel intothe receiving vessel. The reaction mixture was held at 210° C. and 180mmHg for 20 minutes. The pressure was then lowered to 100 mmHg stirredfor an additional 20 minutes after which time the temperature was raisedto 240° C. over a five minute period. The pressure was then lowered to15 mmHg and the reaction mixture was stirred at 240° C. at 15 mmHg for20 minutes. The temperature was then raised to 270° C. over a fiveminute period and the pressure was then lowered to 2 mmHg. The reactionmixture was stirred at 270° C. at 2 mmHg for 10 minutes. The temperaturewas then raised to 310° C. over a ten minute period and the pressure waslowered to 1.1 mmHg. The reaction mixture was stirred at 310° C. at 1.1mmHg for 30 minutes after which the reaction vessel was raised from thesand bath and the molten product polymer was scooped from the reactionvessel into a liquid nitrogen bath in order to quench the reaction.

Data for Examples 1–3 and Comparative Examples 1–5 are gathered in Table1 and illustrate the utility of the method of the present invention. Inthe Comparative Examples 1–5 and Examples 1–3 no p-cumylphenol was addedas a chainstopper. The column heading “DAC” indicates which diarylcarbonate was employed. “DPC” is diphenyl carbonate used inComparative-Example 1 (CE-1). “BMSC” is bis-methyl salicyl carbonate.The ratio “DAC/BPA” represents the initial molar ratio of diarylcarbonate to bisphenol A employed in the reaction. “M_(n)” representsnumber average molecular weight of the product polymer. “Fries level”indicates the concentration of Fries rearrangement product present inthe product polymer. Fries levels were determined by complete solvolysis(KOH catalyzed methanolysis) of the product polymer and quantitativemeasurement of the amount of Fries product, 2-carboxybisphenol A (CASNo. 101949-49-9), present by HPLC. “EC (%)” represents the percentage ofpolymer chain ends not terminating in a hydroxyl group. Hydroxylendgroup concentrations were determined by quantitative infraredspectroscopy. Phenol and salicyl endgroups were determined by HPLCanalysis after product solvolysis.

TABLE 1 REACTION OF BPA WITH DIARYLCARBONATE (DAC) Example DAC DAC/BPAM_(n) Fries level EC(%) CE-1 DPC 1.08 6250 946 41% Example 1 BMSC 1.084293 not detected >99% Example 2 BMSC 1.04 8499 not detected >99%Example 3 BMSC 1.02 13762 not detected 98% CE-2¹ BMSC 1.04 7683 43 CE-3²BMSC 1.04 7892 282 CE-4³ BMSC 1.04 gel 8502 CE-5³ BMSC 1.0 5910 98 47%¹Catalyst was NaOH at 1 × 10⁻⁶ mole per mole BPA ²Catalyst wastetrabutylphosphonium acetate at 2.5 × 10⁻⁴ mole per mole BPA ³Catalystwas lithium stearate at 1 × 10⁻³ moles per mole BPA

Comparative Example 1 highlights differences between melt polymerizationbehavior of DPC and BMSC in reactions with bisphenol A. Meltpolymerization using BMSC (Example 1) affords an undetectable level ofFries product and a very high level of endcapping, whereas meltpolymerization using DPC under the same conditions using the samecatalyst as that used in Example 1 leads to a high level (946 ppm) ofFries product and a far lower endcapping level. Examples 1–3 illustratethe melt polymerization of BMSC with BPA according to the method of thepresent invention which affords polycarbonate containing undetectablelevels of Fries product and very high endcapping levels.

According to the method of the present invention the catalyst comprisesat least one source of alkaline earth ions or alkali metal ions, and atleast one quaternary ammonium compound, quaternary phosphonium compound,or a mixture thereof. Comparative Examples 2 and 3 illustrate thisrequirement. In Comparative Example 2, a source of alkali metal ions,NaOH, was present but no quaternary ammonium compound or quaternaryphosphonium compound was present. In Comparative Example 3, a quaternaryphosphonium compound, tetrabutyl-phosphonium acetate, was present but nosource of alkali metal ions was present. In both instances detectablelevels of Fries product were observed.

The data in Table 1 further illustrate the superiority of the method ofthe present invention over earlier polymerization methods using BMSC.Comparative Examples 4 and 5 show the effect of using lithium stearateat a level (1×10⁻³ mole per mole BPA) taught by U.S. Pat. No. 4,323,668.Comparative Example 4 was run using the protocol used in Examples 1–3and the product polycarbonate showed such a high level of Fries productthat its molecular weight could not be determined due to the very highlevel of branching which occurred. The product polycarbonate wasrecovered as a gel which could not be dissolved for gel permeationchromatography. Comparative Example 5 was run under a milder temperatureregime, the maximum temperature was 260° C. (See below), than that usedin Examples 1–3 and Comparative Examples 1–4, yet nonetheless theproduct polymer contained a significant amount of Fries product, 98 ppm.

Comparative Example No. 5 (CE-5, TABLE 1)

The reactor, equipped and passivated as described above, was charged atambient temperature and pressure with solid bisphenol A (GeneralElectric Plastics Japan Ltd., 0.100 mole) and solid bis-methyl salicylcarbonate (0.100 mole). Lithium stearate catalyst (Kodak, 1×10⁻³ moleper mole bisphenol A) was added as a solid and the reactor wasassembled. The reactor was then evacuated briefly and nitrogen wasreintroduced. The degassing step was repeated three times. The reactorwas then lowered into the sand bath maintained at 150° C. After a fiveminute period stirring at 250 rpm was initiated. These conditions weremaintained for 60 minutes. The temperature of the bath was then raisedto 260° C. The pressure in the reactor was then reduced to 10 mmHg atwhich point the methyl salicylate by-product began to distill from thereaction vessel into the receiving vessel. The reaction mixture was heldat 260° C. and 10 mmHg for 10 minutes after which the reaction vesselwas raised from the sand bath and the molten product polymer was scoopedfrom the reaction vessel into a liquid nitrogen bath in order to quenchthe reaction. The product polycarbonate was characterized by gelpermeation chromatography and found to have M_(w)=14353 and M_(n)=5910.The level of Fries product was determined to be 98 ppm.

As noted, it has been found that the inclusion of an exogenous phenolsuch as p-cumylphenol in the melt reaction of a bisphenol with anester-substituted diaryl carbonate according to the method of thepresent invention affords polycarbonate containing p-cumylphenolendgroups. Data are gathered in Table 2 which demonstrate the surprisingefficiency of this transformation relative to the analogous reactionusing diphenyl carbonate (DPC). Comparative Example 7 illustrates thelow levels of PCP incorporation in the product polycarbonate encounteredwhen a mixture of a bisphenol, DPC and an endcapping agent,p-cumylphenol (PCP) are reacted in the melt. Conversely, Example 5conducted utilizing the method of the present invention reveals a highlevel of PCP incorporation. In the polycarbonate product formed inComparative Example 7 roughly half of the endgroups were found by NMR tobe derived from PCP and half derived from phenol.

TABLE 2 REACTION OF BPA WITH DAC IN THE PRESENCE OF PCP Example DACDAC/BPA PCP M_(n) EC(%) % PCP CE-6 DPC 1.08 — 6250 41% — CE-7 DPC 1.083.05 5674 60% 25% Example 4 BMSC 1.04 — 8499 100% — Example 5 BMSC 1.035.07 9744 99% 97%

Examples 6–12 Polycarbonate Formation (BPA-Resorcinol) Example 6

A glass reactor equipped as described in the General ExperimentalMethods section which had been previously passivated by acid washing,rinsing and drying with nitrogen gas, was charged with 12.15 g of BPA,1.46 g of resorcinol, 25.01 g of BMSC, and 100 μl of an aqueous solutionof TMAH (2.5×10⁻⁴ moles per mole BPA and resorcinol combined) and NaOH(1.5×10⁻⁶ moles per mole BPA and resorcinol combined). Polymerizationwas carried out as described in Examples 1–3 in the following stages:Stage (1) 15 minutes (min), 180° C., atmospheric pressure, Stage (2) 45min, 230° C., 170 mbar, Stage (3) 30 min, 270° C., 20 mbar, and Stage(4) 30 min, 300° C., 0.5–1.5 mbar. After the final reaction stage, thepolymer was sampled from the reaction tube. The percent resorcinol(resorcinol is referred to here as the comonomer) incorporated into theproduct polycarbonate was determined by complete hydrolysis of theproduct polycarbonate followed by HPLC assay of the amount of resorcinoland BPA present in the hydrolysis product. The result of this HPLC assaywas consistent with a polycarbonate comprising repeat units derived fromBPA and resorcinol in a molar ratio of about 82 percent BPA and about 18percent resorcinol. Thus, approximately 90.3 percent of the resorcinolmonomer was incorporated into the product polycarbonate The productpolycarbonate was further characterized by gel permeationchromatography.

Example 7

The polymerization reaction was carried out as in Example 6 but differedin the amount of BMSC used and in the polymerization conditionsemployed. Reagents used were 12.15 g of BPA, 1.47 g of resorcinol, and22.60 g of BMSC. The catalyst was added in 100 μl of an aqueous solutionof tetrabutylphosphonium acetate (TBPA, 2.5×10⁻⁴ per mole BPA andresorcinol combined) and sodium hydroxide (NaOH, 1.5×10⁻⁶ per mole BPAand resorcinol combined). The polymerization was carried out in thefollowing stages: Stage (1) 15 min, 180° C., atmospheric pressure, Stage(2) 15 min, 220° C., 100 mbar, and Stage (3) 10 min, 280° C., 0.5–1.5mbar. The product polycarbonate was characterized by gel permeationchromatography. The percent resorcinol incorporated into the productpolycarbonate was determined as in Example 6. The HPLC assay wasconsistent with a polycarbonate comprising repeat units derived from BPAand resorcinol in a molar ratio of about 81 percent BPA and about 19percent resorcinol. Thus, approximately 94 percent of the resorcinolmonomer was incorporated into the product polycarbonate

Comparative Example 8

The polymerization was carried out as in Example 7 however diphenylcarbonate (DPC) was used instead of BMSC. The amounts of each reagentwere 19.73 g of BPA, 2.38 g of resorcinol, and 25.00 g of DPC. Thecatalyst was TMAH (2.5×10⁻⁴ per mole BPA and resorcinol combined) andsodium hydroxide (NaOH, 1.5×10⁻⁶ per mole BPA and resorcinol combined).The polymerization was carried out in four stages: Stage (1) 15 min,180° C., atmospheric pressure, Stage (2) 60 min, 230° C., 170 mbar,Stage (3) 30 min, 270° C., 20 mbar, and Stage (4) 30 min, 300° C.,0.5–1.5 mbar. The product polycarbonate was characterized as in Example6. The HPLC assay was consistent with a polycarbonate comprising repeatunits derived from BPA and resorcinol in a molar ratio of about 87percent BPA and about 13 percent resorcinol. Thus, approximately 65percent of the resorcinol monomer was incorporated into the productpolycarbonate and about 35 percent of the resorcinol monomer was lost asphenol and excess diphenyl carbonate distilled from the polymerizationmixture.

Example 8

A glass reactor passivated and equipped as described in the GeneralExperimental Methods section was charged with 158.37 g of BPA, 19.10 gof resorcinol, and 295.00 g of BMSC. The catalyst consisted ofethylenediamine tetracarboxylic acid disodium magnesium salt (EDTAMgNa₂)and TBPA. The EDTAMgNa₂ was added (173 μl) as a 0.001 molar solution inwater. TBPA was added in an amount corresponding to about 2.5×10⁻⁴ molesTBPA per mole BPA and resorcinol combined. The reactants wereoligomerized in the following stages: In Stage (1) the reactants wereheated and stirred under an inert atmosphere for 30 minutes at about220° C. at atmospheric pressure. This was followed by a Stage (2) inwhich the temperature was maintained at about 220° C. while the pressurein the reactor was gradually reduced over a period of 20 to 30 minutesto about 30 mbar and afforded a solution of the oligomeric polycarbonatein methyl salicylate. (Methyl salicylate was formed as the by-product ofthe oligomerization reaction.) The mixture was heated at 220° C. and 30mbar until approximately 80% of the methyl salicylate by-product wasremoved. The percent resorcinol comonomer incorporated in the productoligomeric polycarbonate was determined as in Example 6. The HPLC assaywas consistent with an oligomeric polycarbonate comprising repeat unitsderived from BPA and resorcinol in a molar ratio of about 81 percent BPAand about 19 percent resorcinol. Thus, approximately 95 percent of theresorcinol monomer was incorporated into the product oligomericpolycarbonate. The product oligomeric polycarbonate was furthercharacterized by gel permeation chromatography and was shown to have aweight average molecular weight, M_(w), of about 8800 Daltons relativeto polystyrene molecular weight standards.

Example 9

An oligomeric polycarbonate prepared as in Example 8 (but on a largerscale) having a weight average molecular weight, M_(w), of about 8800daltons was ground to a powder and extruded on a WE 20 mm twin screwextruder with three heating zones spanning a temperature range of fromabout 275° C. to about 300° C. The extruder was equipped with two vacuumventing ports to remove methyl salicylate by-product. The temperature ofthe product polycarbonate was about 300° C. at the extruder dieface. Theresidence time in the extruder was approximately 2 minutes during whichtime the lower molecular weight oligomeric polycarbonate was convertedto higher molecular weight polycarbonate. The product polycarbonate wascharacterized by gel permeation chromatography and was found to have aweight average molecular weight of about 20,000 Daltons.

Example 10

The polycarbonate prepared by extrusion in Example 9 (the polycarbonateextrudate) (35.0 g) was placed in a passivated glass reactor equipped asin the General Experimental Methods section and was resubjected to meltpolymerization conditions under the following conditions: Stage (1) 15min, 260° C., atmospheric pressure, Stage (2) 15 min, 280° C., 20–0mbar, and Stage (3) 30 min, 280° C., 0.5 mbar. The product polycarbonatewas characterized by gel permeation chromatography and was found to havea weight average molecular weight of about 26,400 Daltons.

Example 11

The procedure of Example 10 was repeated in an identical fashion exceptthat an additional amount of the metal ion containing catalyst component(30 μl EDTAMgNa₂ (0.001M)) was added to the reaction. The productpolycarbonate was characterized by gel permeation chromatography and wasfound to have a weight average molecular weight of about 35,900 Daltons.

Example 12

The oligomeric polycarbonate prepared in Example 8 (M_(w)=8800 Daltons,35.0 g) was placed in a passivated glass reactor equipped as in theGeneral Experimental Methods section and was resubjected to meltpolymerization conditions under the following conditions: Stage (1) 15min, 260° C., atmospheric pressure, Stage (2) 15 min, 280° C., 20–0mbar, and Stage (3) 30 min, 280° C., 0.5 mbar. The product polycarbonatewas characterized by gel permeation chromatography and was found to havea weight average molecular weight of about 20,800 Daltons.

TABLE 3 PREPARATION OF BPA-RESORCINOL POLYCARBONATES % BPA:% DAC/ %Comonomer Example Comonomer Comonomer DAC DHA¹ M_(w) ² incorporationExample 6 resorcinol 80:20 BMSC 1.14 8400 90.3% Example 7 resorcinol80:20 BMSC 1.03 37200 94.0% CE-8 resorcinol 80:20 DPC 1.08 36500 65.4%Example 8 resorcinol 80:20 BMSC 1.03 8800 95.2% Example 9³ — — — — 20000— Example 10⁴ — — — — 26400 — Example 11⁵ — — — — 35900 — Example 12⁶ —— — — 20800 — ¹Ratio of diaryl carbonate (DAC) to moles of all dihydroxyaromatic compounds (DHA) initially charged. ²Weight Average molecularweight expressed in Daltons are relative to polystyrene molecular weightstandards ³The starting material was an oligomeric polycarbonateprepared as in Example 8. ⁴The starting material was the extrudedpolycarbonate prepared in Example 9. ⁵The starting material was theextruded polycarbonate prepared in Example 9 to which additionalcatalyst was added. ⁶The starting material was the same oligomericpolycarbonate prepared in Example 8.

Examples 6–8 and Comparative Example 8 illustrate an important advantageof the method of the present invention. When BMSC, an ester substituteddiaryl carbonate, was used according to the method of the presentinvention, very high levels of comonomer incorporation into the productpolycarbonate were observed (Example 6: 90.3%, Example 7: 94%, Example8: 95.2%). These high levels of comonomer incorporation into the productpolycarbonate were achieved notwithstanding the high volatility ofresorcinol. The results of Examples 6–8 stand in sharp contrast to theresult in Comparative Example 8 (CE-8) wherein much of the initiallycharged resorcinol comonomer was entrained along with by-product phenolout of the reaction mixture before it could react and becomeincorporated into the product polycarbonate. Thus, only 65.4 percent ofthe initially charged resorcinol was incorporated into the productpolycarbonate when diphenyl carbonate (DPC) was used instead of an estersubstituted diaryl carbonate such as BMSC.

Examples 13–18 and Comparative Examples 9 and 10 Polycarbonate Formation(BPA-Hydroquinone)

The following general experimental procedure was employed in thepreparation of polycarbonates comprising structural units derived fromBPA and hydroquinone (HQ). The melt polymerization reactions werecarried out in a passivated glass reactor equipped as in the GeneralExperimental Methods section. Reactants, BMSC, BPA and HQ, were chargedto the reactor at room temperature. The reactor was then evacuated andflushed with nitrogen three times. The molar ratios given in Table 4 areexpressed as the moles of BMSC per mole of BPA and HQ combined. Forexample, for a polymerization reaction carried out using 1.5 moles ofbis-methyl salicyl carbonate (BMSC), 1.3 moles of bisphenol A (BPA), and0.17 moles of hydroquinone (HQ), the molar ratio of BMSC per mole of BPAand HQ combined would be (1.5 moles BMSC)/(1.3 moles BPA+0.17 moles HQ),or 1.02 moles BMSC per mole of BPA and HQ “combined”. In Examples 13–18the molar ratio ranging of BMSC to BPA and HQ combined was between1.017–1.038 moles of BMSC for each mole of BPA and HQ combined. Thecombined weight of reactants charged to the reactor was sufficient toproduce from about 100 to about 200 grams (g) of product polycarbonate.The alkali metal ion-containing catalyst component was added to thereactor as a 0.005 molar solution of EDTAMgNa₂ in water in an amountcorresponding to concentration of 1×10⁻⁶ mole EDTAMgNa₂ per mole of BPAand HQ combined. The quaternary phosphonium compound catalyst componentwas added as a 40 weight percent solution of TBPA in water in an amountcorresponding to 2.5×10⁻⁴ moles of TBPA per mole of BPA and HQ combined.The melt polymerization reaction was carried out in stages as follows:Stage (1) the reactants were melted and equilibrated at atmosphericpressure under nitrogen at about 180 to about 220° C., Stage (2) vacuumwas applied and methyl salicylate was distilled from the reactionmixture, Stage (3) the polymerization reaction was “finished” by heatingat a final temperature in a range between about 280 and about 300° C.under high vacuum (less than 1 torr). Molecular weights are given inDaltons and were determined by gel permeation chromatography (GPC)relative to polycarbonate molecular weight standards. Compositions inwhich more than about 40 percent of the repeat units were derived fromHQ were insufficiently soluble in chloroform to permit molecular weightmeasurement by GPC without the addition of hexafluoroisopropanol to theanalytical sample comprising the product polycarbonate and chloroform.Levels of residual methyl salicylate in the product polycarbonates weredetermined by gas chromatography. The percent hydroquinone comonomerincorporated in the product polycarbonate was determined by ¹H-NMR.

Data for Examples 13–18 and Comparative Examples 9 and 10 are gatheredin Table 4 below. The data reveal that that the ratio of BPA tohydroquinone initially charged to the reactor was charged was faithfullyreproduced in the composition of the polycarbonate. In general, highlevels of incorporation into the polycarbonate of the relativelyvolatile HQ were observed. Polycarbonate compositions were prepared inwhich between about 10 and about 50 mole percent of all repeat unitswere derived from HQ. Polycarbonate compositions comprising BPA and HQwherein the repeat units derived from HQ comprise more than about 50mole percent of all repeat units present in the polycarbonate were foundto be crystalline. The data further show that only relatively low levelsof residual methyl salicylate are present in the product polycarbonate.The polycarbonates of Comparative Examples 9 and 10 were prepared by thesame general method used in Examples 13 –18 with the exception thatdiphenyl carbonate (DPC) was used instead of BMSC.

TABLE 4 PREPARATION OF BPA-HYDROQUINONE POLYCARBONATES % % BPA DAC/ Mw/Tg % MS⁵ Comonomer Example % HQ¹ DHA² M_(w) ³ M_(n) ³ M_(n) ° C. EC⁴(ppm) incorporation Example 13 90:10 1.017 38000 15900 2.39 149 97 1992% Example 14 80:20 1.028 29300 11800 2.48 144 >99 nd⁶ 95% Example 1580:20 1.030 23900 1020 2.34 142 >99 nd 95% Example 16 80:20 1.033 211009300 2.27 139 nd nd 100% Example 17 60:40 1.035 19800 9000 2.20 133 >9915 94% Example 18 50:50 1.038 20900 6900 3.03 136 nd nd nd CE-9 80:201.100 15200 7200 2.11 nd 87 15⁷ 100% CE-10 80:20 1.030 20200 10100 2.00nd 42 20⁷ 100% ¹Mole percentages of BPA and HQ initially charged to thereactor. ²Ratio of diaryl carbonate (DAC) to moles of all dihydroxyaromatic compounds (DHA) initially charged. ³Weight Average and NumberAverage molecular weights expressed in Daltons are relative topolystyrene molecular weight standards ⁴“% EC” indicates the percent ofproduct polymer chain ends not terminated by a hydroxyl group. ⁵“MS(ppm)” indicates the amount of residual methyl salicylate (MS)by-product present in the product polycarbonate given in parts permillion (ppm). ⁶“nd” indicates that the given value was not determinedfor the indicated polycarbonate ⁷For Comparative Examples 9 and 10 (CE-9and CE-10) which were prepared with diphenyl carbonate instead of BMSCthe values appearing under the heading “MS (ppm)” indicate the amount ofresidual phenol by-product present in the product polycarbonate given inparts per million (ppm).

Examples 19–26 Polycarbonate Terpolymers (Resorcinol, Hydroquinone,4,4′-Biphenol, Methylhydroquinone, BPA)

Polycarbonate terpolymers comprising repeat units from at least threedihydroxy aromatic compounds selected from the group consisting ofresorcinol, hydroquinone, 4,4′-biphenol, methylhydroquinone, andbisphenol A were prepared using the same general method delineated inExamples 13–18. Compositions prepared and relevant physical data aregathered in Table 5 below.

TABLE 5 PREPARATION OF POLYCARBONATE TERPOLYMERS Mole Mole Mole % Mole %Mole % Example % R¹ % HQ BiP² MHQ³ BPA M_(w), M_(n) ⁴ Tg, Tm (° C.)Example 19 20 20 0 60 0 nd⁵  93, 244 Example 20 20 40 0 40 0 nd  97, 265Example 21 0 33 0 33 34 25200, 11200 125, no Tm⁶ Example 22 0 60 0 10 30nd 131, 320 Example 23 0 0 33 33 34 34500, 15900 141, no Tm Example 24 00 20 60 20 25200, 11500 117, no Tm Example 25 10 50 0 0 40 18400, 7300125, 290 Example 26 20 40 0 0 40 21300, 9100 121, no Tm ¹“R” denotesresorcinol. ²“BiP” demotes 4,4′-biphenol. ³“MHQ” denotesmethylhydroquinone ⁴M_(w) and M_(n) denote the Weight Average molecularand Number Average molecular weight respectively of the productterpolymers and the values are expressed in Daltons relative topolystyrene molecular weight standards. ⁵“nd” indicates that the givenvalue was not determined for the indicated polycarbonate terpolymer.⁶For The term “no Tm” is used to indicate polycarbonate terpolymerswhich were amorphous and hence possessed no melting point (Tm)..

The data for the terpolymers illustrates the general utility of thepresent invention in the preparation of polycarbonates comprising repeatunits derived from at least three different dihydroxy aromaticcompounds. The data reveal that the method may be used to prepare bothcrystalline (Examples 19, 20, 22, and 25) and amorphous (Examples 21,23, and 26) polycarbonate terpolymers. The polycarbonate terpolymerspossess both a high level of endcapping and very low levels of Friesproduct.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood by thoseskilled in the art that variations and modifications can be effectedwithin the spirit and scope of the invention.

1. A polycarbonate prepared by melt polymerization reaction of anester-substituted diaryl carbonate with a dihydroxy aromatic compound,said polycarbonate comprising repeat units derived from the dihydroxyaromatic carbonate coupled via internal carbonate and ester carbonatelinkages, and terminal hydroxyl and hydroxyl ester groups, wherein saidpolycarbonate has: (a) a weight average molecular weight of between10,000 and 100,000 Dalton; (b) less than 1% of chain ends bearing freehydroxy groups, less than 100 parts per million Fries product; (c) lessthan 1 mole percent of internal ester carbonate linkages relative tototal number of moles of dihydroxy aromatic compound reacted; and (d)less than 1 mole percent of terminal hydroxy ester groups relative tototal number of moles of dihydroxy aromatic compound reacted.
 2. Thepolycarbonate of claim 1 wherein said polycarbonate has a weight averagemolecular weight of between 15,000 and 60,000 Daltons.
 3. Thepolycarbonate of claim 1 wherein said ester-substituted diaryl carbonateis selected from the group consisting of bis-methyl salicyl carbonate,bis-ethyl salicyl carbonate, bis-propyl salicyl carbonate, bis-butylsalicyl carbonate, and bis-benzyl salicyl carbonate.
 4. Thepolycarbonate of claim 1 wherein said ester-substituted diaryl carbonateis bis-methyl salicyl carbonate.
 5. The polycarbonate of claim 1 whereinthe polycarbonate further comprises endgroups derived from an exogenousmonofunctional phenol.
 6. The polycarbonate of claim 5 wherein theexogenous monofunctional phenol is selected from the group consisting of2,6-xylenol, p-t-butylphenol, p-cresol, cardanol, p-cumylphenol,p-nonylphenol, p-octadecylphenol, 1-naphthol, and 2-naphthol.
 7. Thepolycarbonate of claim 1 wherein the polycarbonate is a polyestercarbonate.
 8. The polycarbonate of claim 1 wherein the dihydroxyaromatic compound is selected from the group consisting of resorcinol,methylresorcinol, hydroquinone, and methylhydroquinone is reacted toprepare the polycarbonate.
 9. The polycarbonate of claim 1 wherein thepolycarbonate is a copolycarbonate wherein a first dihydroxy aromaticcompound and a second dihydroxy aromatic compound are reacted to preparethe polycarbonate, and wherein the first dihydroxy aromatic compound isselected from the group consisting of resorcinol, methylresorcinol,hydroquinone, and methylhydroquinone, the second aromatic dihydroxycompound is different from the first aromatic dihydroxy compound and isselected from the group consisting of resorcinol, methylresorcinol,hydroquinone, methylhydroquinone, bisphenols having the structure

wherein R⁵–R¹² are independently a hydrogen atom, halogen atom, nitrogroup, cyano group, C₁–C₂₀ alkyl radical, C₄–C₂₀ cycloalkyl radical, orC₆–C₂₀ aryl radical, W is a bond, an oxygen atom, a sulfur atom, a SO₂group, a C₆–C₂₀ aromatic radical, a C₆–C₂₀ cycloaliphatic radical, orthe group

wherein R¹³ and R¹⁴ are independently a hydrogen atom, C₁–C₂₀ alkylradical, C₄–C₂₀ cycloalkyl radical, or C₄–C₂₀ aryl radical, or R¹³ andR¹⁴ together form a C₄–C₂₀ cycloaliphatic ring which is optionallysubstituted by one or more C₁–C₂₀ alkyl, C₆–C₂₀ aryl, C₅–C₂₁ aralkyl,C₅–C₂₀ cycloalkyl groups, or a combination thereof; dihydroxy benzeneshaving structure III

wherein R¹⁵ is independently at each occurrence a hydrogen atom, halogenatom, nitro group, cyano group, C₂–C₂₀ alkyl radical, C₄–C₂₀ cycloalkylradical, or a C₄–C₂₀ aryl radical, and d is an integer from 1 to 4; anddihydroxy naphthalenes having structures IV and V

wherein R¹⁶,R¹⁷,R¹⁸ and R⁹ are independently at each occurrence ahydrogen atom, halogen atom, nitro group, cyano group, C₁–C₂₀ alkylradical, C₄–C₂₀ cycloalkyl radical, or a C₄–C₂₀ aryl radical, e and fare integers of from 0 to 3, g is an integer from 0 to 4, and h is aninteger from 0 to
 2. 10. The polycarbonate of claim 9 wherein the firstaromatic dihydroxy compound is resorcinol and the second aromaticdihydroxy compound is 2,2-bis(4-hydroxyphenyl)propane (i.e. bisphenolA).
 11. The polycarbonate of claim 9 wherein said polycarbonate has aweight average molecular weight of between 15,000 and 60,000 Daltons.12. The polycarbonate of claim 9 wherein said ester-substituted diarylcarbonate is selected from the group consisting of bis-methyl salicylcarbonate, bis-ethyl salicyl carbonate, bis-propyl salicyl carbonate,bis-butyl salicyl carbonate, and bis-benzyl salicyl carbonate.
 13. Thepolycarbonate of claim 9 wherein said ester-substituted diaryl carbonateis bis-methyl salicyl carbonate.
 14. The polycarbonate of claim 9wherein the polycarbonate further comprises endgroups derived from anexogenous monofunctional phenol.
 15. The polycarbonate of claim 14wherein the exogenous monofunctional phenol is selected from the groupconsisting of 2,6-xylenol, p-t-butylphenol, p-cresol, cardanol,p-cumylphenol, p-nonylphenol, p-octadecylphenol, 1-naphthol, and2-naphthol.
 16. The polycarbonate of claim 9 wherein the polycarbonateis a polyester carbonate.
 17. A formulation comprising: a polycarbonateprepared by melt polymerization reaction of an ester-substituted diarylcarbonate with a dihydroxy aromatic compound, said polycarbonatecomprising repeat units derived from the dihydroxy aromatic carbonatecoupled via internal carbonate and ester carbonate linkages, andterminal hydroxyl and hydroxyl ester groups, wherein said polycarbonatehas: (a) a weight average molecular weight of between 10,000 and 100,000Dalton; (b) less than 1% of chain ends bearing free hydroxy groups, lessthan 100 parts per million Fries product; (c) less than 1 mole percentof internal ester carbonate linkages relative to total number of molesof dihydroxy aromatic compound reacted; and (d) less than 1 mole percentof terminal hydroxy ester groups relative to total number of moles ofdihydroxy aromatic compound reacted; and one or more additionalcomponents selected from the group consisting of heat stabilizers, moldrelease agents, UV stabilizers, polycarbonates, polyestercarbonates,polyesters and olefin polymers.
 18. A molded article formed frompolycarbonate prepared by melt polymerization reaction of anester-substituted diaryl carbonate with a dihydroxy aromatic compound,said polycarbonate comprising repeat units derived from the dihydroxyaromatic carbonate coupled via internal carbonate and ester carbonatelinkages, and terminal hydroxyl and hydroxyl ester groups, wherein saidpolycarbonate has: (a) a weight average molecular weight of between10,000 and 100,000 Dalton; (b) less than 1% of chain ends bearing freehydroxy groups, less than 100 parts per million Fries product; (c) lessthan 1 mole percent of internal ester carbonate linkages relative tototal number of moles of dihydroxy aromatic compound reacted; and (d)less than 1 mole percent of terminal hydroxy ester groups relative tototal number of moles of dihydroxy aromatic compound reacted.